There is known an internal combustion engine of a vehicle, which is provided with an EGR device to recirculate a portion of exhaust gas as EGR gas to an intake passage for the purpose of improving fuel consumption and reducing knocking and exhaust emissions of the internal combustion engine.
However, in the internal combustion engine, which is provided with the EGR device, even when an EGR valve is closed at the time of driving a throttle valve to a closing side thereof (at the time of controlling an opening degree of the throttle valve to a closing side), the EGR gas may remain in a portion of an EGR passage located on a downstream side of the EGR valve or in the intake passage in a system. Particularly in a system, which recirculates the EGR gas to a portion of the intake passage located on the upstream side of the throttle valve, a large quantity of the EGR gas may remain in the portion of the intake passage located on the upstream side of the throttle valve. Therefore, in such a system, the quantity of the EGR gas, which flows into a cylinder of the internal combustion engine at the time of decelerating the engine (thereby decelerating the vehicle) or the time of reaccelerating the engine (thereby reaccelerating the vehicle), may be excessively increased to cause a deterioration of a combustion state, thereby possibly resulting in occurrence of misfire.
In view of the above point, JP2010-36780A teaches a technique of limiting combustion deterioration in the internal combustion engine. Specifically, according to the technique of JP2010-36780A, a throttle valve is closed at a speed that is slower than an upper limit valve closing speed, above which the misfire will likely occur (i.e., the throttle opening degree being reduced at a speed that is lower than an upper limit closing speed, above which the misfire will likely occur). In this way, the combustion deterioration is limited.
Here, it should be noted that depending on the operational state immediately before the time of decelerating the engine, a large quantity of EGR gas may be already present in the intake passage at the time of starting the deceleration of the engine. However, technique of JP2010-36780A is a technique that limits the suctioning of the EGR gas by closing the throttle valve at the speed, which is lower than the upper limit closing speed of the throttle valve, and thereby limiting a rapid decrease of the intake conduit pressure (a rapid increase of an intake conduit negative pressure). In the case where the large quantity of EGR gas is already present in the intake passage at the time of starting the deceleration of the engine, the quantity of the EGR gas, which flows into the cylinder, becomes excessively large according to this technique, thereby possibly resulting in misfire. Furthermore, the above technique cannot counteract with a case where the EGR gas remains in the intake passage until the time of reaccelerating the engine after the execution of the deceleration of the engine, thereby possibly resulting in occurrence of misfire at the time of reacceleration of the engine.